Interpretive Summary: The Hourani landrace is the evolutionary link between wild emmer wheat, the wild progenitor of all domesticated wheats, and the advanced wheat cultivars. The landrace was cultivated for millennia in the Houran plateau of northern Jordan and southern Syria as a source of flat bread and grain-based products. Since the 1980s, however, it became highly fragmented due to the introduction of high yielding varieties and new cropping systems. Its cultivation has declined due to its low yield potential and susceptibility to foliage diseases as compared to high yielding varieties. Its genetic structure was assessed in 289 populations collected from ten villages in four ecogeographical regions in the arid and semi-arid regions of Jordan and Syria. The results indicate that the landrace is composed of genetically heterogeneous populations which have evolved in a multitude of environments and local farming systems. The patterns of variation identified in this study suggest that the landrace represented a largely untapped reservoir of useful traits and trait combinations for adaptation to drought. Multivariate analyses of a set of agronomic, qualitative and storage protein markers confirmed the existence of a highly divergent germplasm in this landrace, especially at the village level, for agronomic and spike qualitative traits. The germplasm and the data collected in the course of this study are of immediate value to farmers and breeders who are interested in selecting parent material for combined wide adaptation and higher biomass and grain yield under relatively dry conditions.

Technical Abstract:
The Hourani durum wheat landrace was cultivated for millennia in the Houran plateau of northern Jordan and southern Syria as a source of flat bread and grain-based products. Since the 1980s, however, it became highly fragmented due to the introduction of high yielding varieties and new cropping systems. Its genetic structure was assessed in 289 populations collected from ten villages in four ecogeographical regions in both countries. Ten agronomic and 10 polymorphic qualitative descriptors in addition to polymorphism at two high-molecular-weight (HMW) glutenin loci were used in this study. Polymorphism in agronomic traits was apportioned among populations (13.54%), among villages (56.39%), among ecogeographical regions (21.05%) and among countries (9.02%). The respective values for qualitative descriptors were 8.23, 20.74, 47.95 and 23.08%. Population differentiation at the HMW glutenin loci was 24.85% for the whole collection and no significant differences were detected among or within countries. Geographical distances among villages were correlated with genetic distances based on agronomic (r=0.59, p=0.05) and qualitative (r=0.43, p=0.08) traits; genetic distances of the last two, however, were highly correlated (r=0.92, p=0.000). Based on agronomic traits, only 20% of the populations had all 10 principal components (CPCs) in common; almost half (53.0%) shared six-eight, whereas the remaining 27% shared zero-three CPCs. Average correct classification of germplasm by country (82.0%), region (70.0%) village (51.0%) and population (35.7%), based on the discriminant power of different agronomic traits and trait combinations, confirms the existence of a highly divergent germplasm in this landrace.